Field of the Invention
The present invention relates to an image forming apparatus configured to control an input current to a heater placed in a fixing part by pulse width modulation (PWM).
Description of the Related Art
A conventional image forming apparatus of this type is described in JP 2009-69371 A mentioned below. In the image forming apparatus, a rectifier circuit converts an alternating current supplied from a commercial power supply to a direct current. An inverter circuit generates an alternating current from a direct current generated in the rectifier circuit, by switching a switching element on and off in a duty cycle specified by a control signal from a control part. The generated alternating current is supplied to the heater. In this manner, the input current to the heater is controlled.
Meanwhile, a known chopper circuit is also applicable to PWM control of the heater. The chopper circuit includes a switching element, a freewheeling element (a diode), and a reactor. The chopper circuit operates in a continuous current mode when driving the switching element in a high duty cycle (for example, at the time of printing). In the continuous current mode, problems may occur such as generation of recovery noise in the freewheeling element, and a temperature rise in the switching element due to switching loss.